Daphlongeranine B belonging to the Daphniphyllum alkaloids has an unprecedented and unique hexacyclic ring system and has seven stereogenic centres of which three are fully functionalised carbon centres. It represents an attractive and as yet unmet synthetic challenge.A model of the advanced spiro intermediate 1  was synthesised in 9 steps (figure 1) starting from commercial L-proline. Amide coupling and nitration was followed by an intramolecular Michael addition step which successfully yielded the tricyclic core 2   of Daphlongeranine B.

Synthesis towards daphlongeranine B

245th National Meeting (2013)

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